Time-Restricted Eating - A Good Idea?

Athletes are always in search of interesting and effective methods to control their weight. A popular trend currently is the combination of sports and intermittent fasting. Recent research suggests that this dietary approach has favorable effects on our metabolism, disease prevention, and gut flora. Studies have been conducted with healthy, moderately active individuals, as well as those with various conditions (e.g., diabetes, obesity, elevated cholesterol levels). There are indications that intermittent fasting also supports weight loss and a reduction in fat mass. However, there are no studies conducted specifically with athletes.

When searching on the internet, various approaches can be found, such as fasting one day a week, alternate-day fasting, or fasting every third day—where individuals can eat whatever they want on one day but abstain from energy intake on the fasting day. It is important to mention that, in almost all studies on intermittent fasting, energy intake is not reduced.

A specific form of intermittent fasting is Time Restricted Eating. The 8/16 method (eating within an 8-hour window and fasting for the remaining 16 hours) is a widespread form, but there are other less or more restrictive forms ranging from 6/18 to 10/14.

What is the best solution? 6/18 or 10/14?

There are various approaches to Time Restricted Eating. The most common is probably the 8/16 method. Those following this pattern can eat within an eight-hour window and fast for the remaining 16 hours of the day. Depending on when breakfast is consumed, this could mean finishing eating by 3 pm if breakfast was at 7 am. While this approach may be feasible for some, an eight-hour window can be quite tight for athletes, especially those who train twice a day, and some may even train late in the evening. In such cases, the second session of the day may fall into the fasting period, leaving the body in a deficit until it receives energy again. Moreover, this delayed intake also means that recovery processes take longer compared to those who eat afterward.

With a stricter form like the 4/20 method (Warrior Diet), the challenge becomes even greater. Meeting nutritional needs is challenging with such a short time frame, especially for those training multiple hours daily. Additionally, supporting training with sufficient energy becomes difficult. Another challenge is the impact on the normal lifestyle of individuals. What does one do when invited to friends' gatherings, but the 4-hour window has already passed? This approach is not very realistic and poses social challenges.

A slightly more relaxed method with a 10 or 12-hour window seems more reasonable. The 8/16 rhythm may work for some, but the 10/14 or 12/12 method allows for greater flexibility in timing energy intake.

Time Restricted Eating for Athletes?

When we think of elite athletes, they typically undergo intense training phases. Training is demanding, and effective recovery is crucial, including specific steps such as the consumption of food post-exercise. The immune system of an athlete is heavily taxed, leading to increased inflammation markers in the body, and nutrition plays a vital role in navigating these metabolic situations to maintain health. If energy intake is severely time-restricted, it is likely to impact both performance and health. Moreover, the narrow time window raises the risk of not consuming sufficient energy. This issue, insufficient calorie intake (low energy availability), is a significant concern in competitive sports. Athletes expend a considerable amount of energy, and it becomes challenging to eat enough when there is limited time for it.

A severely restricted energy intake increases the risk of low energy availability. The more we limit our nutrition, the higher the likelihood that our body will not be adequately supplied. The energy demands of an athlete are substantial. If energy intake is severely time-restricted, it will not cover the calorie expenditure.

Of course, there are days when one goes out and completes a session on an empty stomach to provoke certain metabolic adaptations, which are well documented in endurance athletes. However, it's essential to remember that there is much more evidence supporting the positive impact of energy intake around training. Having more time to eat also has the advantage of minimizing the risk of low energy availability.

It is also important to note that there are no studies on Time Restricted Eating in elite athletes. Furthermore, there is a lack of studies proving that this diet has performance-enhancing effects. Considering the potential negative impact on performance, it is premature to recommend this dietary approach to athletes engaging in extensive training. A 12/12 pattern might be more reasonable (in some situations), but it must be ensured that there is sufficient time for energy intake and optimal support for recovery. Before implementing any form of Time Restricted Eating, it is strongly advisable to consult with an expert, such as a nutritionist, to assess whether this diet can meet the energy and nutrient requirements without compromising performance.

Additional literature:

Di Francesco et al. (2018) A time to fast. Science, 362, 770-775.

Levy & Cho (2019) Intermittent fasting and its effects on athletic performance. Current Sports Medicine Reports, 18, 266.269. doi: 10.1249/JSR.0000000000000614

Manoogian & Panda (2017) Circadian rhythms, time-restricted feeding, and healthy aging. Ageing Research Reviews, 39, 59-67. doi.org/10.1016/j.arr.2016.12.006

Moro et al. (2016) Effects of eight weeks of time-restricted feeding (16/8) on basal metabolism, maximal strength, body composition, inflammation, and cardiovascular risk factors in resistance-trained males. J Transl Med, 14:290. doi: 10.1186/s12967-016-1044-0

Peos et al. (2019) Intermittend Dieting: Theoretical Considerations for the Athlete. sports, 7, 22. doi:10.3390/sports7010022